The present invention relates to a method of driving a stepping motor and more particularly, to a technique of restraining vibration of the stepping motor during drive thereof.
Conventionally, the stepping motor is used in an automotive suspension system disclosed, for example, in JP-A 5-193327.
A variable-damping-force-type shock absorber used in the automotive suspension system includes a rotary valve having changeable damping force characteristic, and a stepping motor mounted at an upper end of the shock absorber so as to rotate the rotary valve.
However, the conventional variable-damping-force-type shock absorber has the following inconvenience:
When driving stepwise the stepping motor, drive current is always turned on, i.e. in the continuous turn-on state, actual current input to the stepping motor is heavy, and thus drive torque is great. As a result, great vibration noise is produced upon drive of the stepping motor, which may cause a seat occupant to have a strange feel upon low-speed cruising or standstill of a motor vehicle in particular.
It is, therefore, an object of the present invention to provide a method of driving a stepping motor which contributes to a restraint of generation of vibration during drive thereof.